For correct diagnosis of various diseases, e.g. cancer, biopsies are often taken. This can either be via a lumen of an endoscope or via needle biopsies. In order to find the correct position to take the biopsy, various imaging modalities are used such as X-ray, MRI and ultrasound. In case of e.g. prostate cancer in most cases the biopsy is guided by ultrasound. Although helpful, these methods of guidance are far from optimal. The resolution is limited and, furthermore, these imaging modalities can in most cases not discriminate between benign and malignant tissue. As a result a physician does not know for certain that from the correct part of the tissue a biopsy is taken. Thus, the physician takes almost blind biopsies and even if after inspection of the tissue no cancer cells are detected, one does not know for certain that simply the right spot to take the biopsy was missed.
In order to improve the biopsy procedure direct inspection of the biopsy position prior of taken the biopsy is required. A way to achieve this is by microscopic inspection at this position. This requires a miniaturised confocal microscope. For even more detailed tissue inspection non-linear optical techniques allow high molecular contrast without the need of staining the tissue (see J. Palero et al. SPIE vol. 6089 (2006) pp. 1A1-1A11). These techniques are based on two-photon and second harmonic spectral imaging. In order to make the scanner compatible with these non-linear techniques photonic crystal fibers should be employed with large core diameters in order to reduce non-linear effects in the optical fiber itself. Nevertheless, the collection efficiency for two-photon imaging or other non-linear optical techniques may be low. One way of increasing the collection may be to increase the solid angle extended by the optical fiber. L. Fu, X. Gan and M. Gu, in “Nonlinear optical spectroscopy based on double-clad photonic crystal fibers”, Optics Express 13 (2005) 5528, for example shows how to increase collection efficiency significantly by exploiting the inner cladding and the core of the double-clad photonic crystal fiber (PCF). However, the resulting numerical aperture is still rather low for practical applications.
Hence, an improved optical probe would be advantageous, and in particular a more efficient and/or reliable optical probe would be advantageous.